In-situ evaluation of an interior suspended-film multi-cavity glazing retrofit for existing curtain-wall buildings

This study proposed a glazing retrofit system (hereafter GR system) in which an interior suspended-film unit was added to an existing Low-E double-glazed curtain-wall assembly to form a multi-cavity assembly, and experimentally evaluated its short-term winter thermal performance. Unlike previous studies that relied on laboratory hot-box measurements or numerical simulation, this work provides in-situ measurement, using the average method of ISO 9869-1, of center-of-glazing thermal transmittance, surface-temperature distributions, and heat-mode energy consumption under real winter boundary conditions. The retrofitted assembly comprised five layers with four cavities and two low-emissivity coatings acting in series. Two adjacent full-scale test rooms (3.6 m × 5.4 m × 2.7 m) in Goyang, South Korea, were monitored simultaneously over 72 h under a controlled heating schedule of 8 h per day, with semi-outdoor air temperatures from −9.38 to −1.49 °C. The glazed façade faced an unconditioned semi-outdoor space and received no direct solar radiation, thereby minimizing the influence of direct solar gains and allowing the conductive component to be evaluated separately. The measured center-of-glazing U-value decreased from 1.738 to 0.347 W/m 2 ·K, a reduction of 80.0%. This reduction applies to the center of glazing only; the existing aluminum frame was unchanged, so the improvement at whole-window level is smaller. The indoor-side glazing surface temperature increased by 2.4 K at the center and 3.0 K at the edge during heating, while the average indoor-side frame surface temperature decreased by 2.6 K. Whole-window heat-loss decomposition indicated that the retained frame became the single largest heat-loss path after the retrofit and bounds the benefit obtainable from a glazing-only intervention. Daily heat-mode energy use was reduced by 10.9%, and by 12.1% after normalization for the indoor-outdoor temperature difference; an indicative annual simulation for a reference office building, not validated against these measurements, gives a heating energy reduction of 11.5–15.8%.